a) Field of the Invention
The present invention relates to a golf club and a method for manufacturing the same.
b) Prior Art
As disclosed in Japanese Registered Patent Publication No.2560272, it is known art to provide an iron golf club which comprises a face member, a head body having an aperture on a front surface for securing the face member thereto, a cavity on a rear surface and a shaft attachment portion on one side; and a shaft connected thereto.
Recently, the main currents of iron golf clubs have been directed to the use of a cavity-back type head. The cavity-back configuration is aimed at enlarging a moment of inertia by concaving a middle portion of a rear face of a head so as to distribute the weight toward a periphery thereof, thus decreasing the deviation of travelling directions of balls caused by so-called off-center shots. According to conventional golf clubs, club heads are relatively long in the toe-to-heel direction, and thus, cavities thereof eventually become too long in the same direction, so that there is a problem that it is difficult to obtain a great repulsive force by resiliently bending a face of the head.
Further, an improved cavity-back type head with an undercut configuration is also known art. Such undercut configuration is aimed at making the center of gravity deeper by further hollowing a cavity toward the sole direction, which also contributes to enlarging a resiliently bending area on a face, improving a repulsive force against balls.
For methods of manufacturing a head with such undercut configuration, an insert die method wherein an insert die is used as a partial die for a cavity forming portion, a machining method wherein a golf club with a face on a front surface and a cavity on a rear surface is produced by machining, said cavity being machined from a rear side to form the undercut configuration.
According to conventional methods, however, there are limitations to the depth and configuration to be hollowed. Namely, according to the insert die method, the insert die must be removed after forming, but too deep undercut disenables the removal of the insert die. Further, according to the machining method in which machining is performed from a rear surface of a head, machining tools such drills often do not reach the depth of a cavity and is likely to damage other portions. In other words, according to these conventional methods, the undercut configuration is not free to form, thus leading to the restricted degree of freedom relative to the positional setting of the center of gravity of a head, making it difficult to insure an effective configuration and area on a face which is to be resiliently bent.
In the meantime, for the above-mentioned iron golf club comprising a face member; a head body having an aperture on a front surface for securing the face member thereto, a cavity on a rear surface and a shaft attachment portion on one side; and a shaft connected thereto, is used welding, specifically laser beam welding as a means for securing the face member to the aperture, as laser beam welding is advantageous in directional maneuverability.
However, when components are welded to each other with one component being flush with the other, the middle portion of the welded portion rises while both ends thereof sink due to being attracted by heat. Further, as laser beam welding realizes such rapid heating and rapid cooling that bubbles generated inside the welded portion are confined within the same before they come out to the external, so that pin holes appear on the surface when polishing a club head at a later stage. Such problems occur noticeably in the case of partial welding in which penetration does not reach a rear surface.
Accordingly, it is a main object of the present invention to provide a golf club with a larger degree of freedom in designing the same so that a face may be easily bent resiliently and a head may have a lowered center of gravity.
It is another object of the invention to provide a method for manufacturing a golf club with such larger degree of freedom.
It is a further object of the invention to provide a method for manufacturing a golf club which can protect a golf club against sinks and/or pin holes generated when performing laser beam welding.
To attain the above objects, there is provided, in accordance with from a first aspect of the invention, a golf club which comprises: a head which has a face on a front surface, a shaft attachment portion at one side and a cavity on a rear surface, said cavity having a bottom surface defined by a maximum length H1 in a top-to-sole direction and another maximum length W1 in a toe-to-heel direction; and a shaft connected to the head, wherein the cavity is formed to satisfy an inequality: H1/W1xe2x89xa70.6.
Further, from a second aspect of the invention, there is provided a golf club which comprises: a head which has a face on a front surface, said face having a maximum length H2 in a top-to-sole direction, a shaft attachment portion at one side and a cavity on a rear surface, said cavity having a bottom surface defined by a maximum length H1 in a top-to-sole direction; and a shaft connected to the head, wherein the cavity is formed to satisfy an inequality: 0.7xe2x89xa6H1/H2xe2x89xa60.85.
With above-structured golf club, there can be provided a golf club with a larger degree of freedom in designing the same so that a face may be easily bent resiliently to give a greater repulsive force against balls.
According to another aspect of the invention, there is provided a method for manufacturing a golf club, said golf club comprising: a head having a face on a front surface and a shaft attachment portion at one side, said head being formed by combining a plurality of members; and a shaft connected to the head, said method comprising the steps of: forming a beveled portion on a rear surface of one of said combining members; and then joining the members together by welding. Accordingly, a relief space for bubbles generated during the laser beam welding is insured, said bubbles being able to escape through the relief space by means of the penetration welding relative to the partially thinned portion.